The Student Room Group
Reply 1

8HI(g) + H2SO4 → 4I2(g) + H2S(g) + 4H22O(l)
Iodine is a strong reducing agent , so it oxidises itself losing electrons to form Iodine and it reduces sulpher which form hydrogen sulhpide and the rest rect to form water.
Reply 2
According to my revision book the reaction goes,

2HI(g) + H2SO4(aq) → SO2(g) + I2(g) + 2H2O(l)

Then further reduction to H2S:
6HI + SO2(g) → H2S(g) + 3I2(s) + 2H2O(l)
Reply 3
There are three

NaI + H2SO4 --> HI + NaHSO4 then the HI goes onto reduce the SO42-
2HI + H2S04 --> SO2 + I2 + 2H2O then HI reduces the SO2
6HI + SO2 --> H2S + 3I2 + 2H2O

It is a progressive reduction
NaBr does only the first two (with Br instead of I)
NaCl does only the first one (with Cl instead of I)

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